The Holy Grail of Energy Storage

You don’t have to spend much time looking into the energy scene, particularly around renewables, to find a statement to the effect that “energy storage is the key”.   Of course, what is actually meant is that the increasing use of renewables such as wind power, will make storage of electricity more important as a way of counteracting the fact that renewables are intermittent in output and may not produce electricity when it is needed.  This has become one of those energy truisms that gets trotted out regularly along with “you can’t store electricity”, which is rather odd when we all use a plethora of electricity storage devices (batteries) everyday.  What we really mean is that you can’t store electricity as electricity, it has to be stored in some other way – in the chemistry of a battery, the potential energy of a pumped hydro power station, the kinetic energy of a fly wheel, compressed air in a tank, or some other medium.  In fact even that statement isn’t correct as we can store electricity directly in a super-conducting coil which has no electrical resistance, commercial superconducting machines are available and find niche applications.

The electricity storage options most talked about are; pumped hydro power stations, (I remember visiting Ffestiniog pumped hydro scheme aged 10 or 11 – perhaps one of the sources of my interest in energy), flywheels, batteries of all types of course, compressed air, capacitors and super-capacitors, flow batteries and superconducting devices.   Each has a range of power rating – varying from kW to GW – discharge times (seconds to hours), efficiencies, capital costs, stage of technology development and ease of deployment.  But one of the most interesting energy storage technologies that until recently got very little attention is liquid air.  Highview Power (http://highview-power.com/wordpress/) have been running a grid-connected unit next to the SSE power station in Slough for more than 18 months.  As well as storage applications the technology can be used for waste heat to power (what I call WHP) applications and combined cold and power (CCP as opposed to CHP?).   WHP using various technologies is a major opportunity and a large resource that is currently largely being ignored.

As well as energy storage, liquid air technologies can also address two other important and valuable applications:

–       providing a fast-refueling and low-carbon transport fuel that is zero-emission at the point of use

–       harvesting low-grade waste heat.

In fact, just as people used to talk a lot about the “hydrogen economy”, it is possible to think about a liquid air economy.  Environmental and economic benefits can be increased by integrating liquid air technologies across the electricity, gas, transport and industrial sectors.  Unlike the hydrogen economy, which has been a dream since Jules Verne wrote about it in the 1870s – and in my opinion is likely to remain a dream, the technology required for a liquid air economy is a lot closer to existing (indeed much of it exists already), the engineering problems are easier to solve, and the new infrastructure deployment required is much less daunting.

Dearman Engines (http://www.dearmanengine.com), which is out of the same stable as Highview, is developing a liquid air engine and with partners including MIRA, Air Products and Loughborough University and has won a grant from the Technology Strategy Board to build and test an engine fitted into a commercial vehicle.  This will be a refrigerated truck with the Dearman engine providing cooling and power, it will be the world’s first liquid air commercial vehicle.

Although, as has been acknowledged by the Centre for Low Carbon Futures in an October 2013 report, “Liquid air technologies – a guide to the potential”, liquid air technologies are not a “silver bullet” they do have a number of advantages including utilizing existing components and supply chains.  This alone makes them worthy of further research – and it now seems as if that research is gearing up.  The University of Birmingham has won a £6m grant to create the Birmingham Centre for Cryogenic Energy Storage.  (Always good to see my Alma Mater doing pioneering work!).

Liquid air is one of those technologies that has long been neglected but thanks to the pioneering and world leading work of Dearman, Highview and their partners, is now starting to make real advances towards commerciality.  As well as the clear technical advantages it has a real appeal in its circularity and conceptual simplicity (although of course turning concepts into real engineering and economically viable products is never simple).  Although there can never be a single silver bullet solution to our energy problems it looks like liquid air has an important role to play.

For more on liquid air see the following:

http://liquidair.org.uk/about-liquid-air

http://liquidair.org.uk/full-report

http://liquidair.org.uk/raeng-clcf-conference/raeng-clcf-presentations

http://liquidair.org.uk/flipbook/files/inc/67c183d322.pdf